1. Field of the Invention
This invention is concerned with catalytic cracking processes, specifically fluid catalytic cracking (FCC) processes of high-temperature, short residence time to considerably lower coke make in the FCC unit.
2. Description of the Prior Art
The field of catalytic cracking has undergone progressive development since 1940. The trend of development from the thermofor catalytic cracker (TCC) to the widespread use of the fluid catalytic cracking (FCC) process is evident from both patent and technical literature. The trend in FCC processes has been to all riser cracking, use of zeolite-containing catalyst, heat balanced operation, and complete combustion of CO to CO.sub.2 within the regenerator. A typical FCC unit and process including a regenerator for the spent catalyst, is disclosed in U.S. Pat. No. 4,368,114, the disclosure of all of which is herein incorporated by reference. This patent, typical of FCC processes, utilizes the concept of a circulating catalyst inventory wherein catalyst is contacted with the feedstock under catalytic cracking conditions so as to form a mixture of products as the catalyst and feedstock move through the reaction zone, typically upwards in a riser reactor. During the aforementioned catalytic cracking, coke is deposited on the catalyst thereby reducing its activity. This coke laden catalyst, also known as spent catalyst, is separated from the reaction products, either by cyclonic separator means and/or by stripping with a stripping gas and is then in a state suitable for regeneration. The spent catalyst is fed to a regeneration unit where it is contacted with an oxygen-containing combustion gas under conditions of time, temperature and pressure sufficient to reduct the coke on the catalyst to about 0.25% or less while forming combustion products comprising CO and CO.sub.2. At least a portion of the resulting regenerated catalyst is again contacted with fresh feedstock, thereby completing the cycle.
As is evident from the foregoing, the regeneration process is not only energy intensive but produces undesirable combustion products such as CO and CO.sub.2. Additionally, the conventional FCC units operate under such conditions whereby approximately 5% of the feedstock is burned in a regenerator to supply the heat of cracking. Thus, the heat balance in conventional FCC units are inefficient and reduce the ultimate FCC yield as well as greatly limiting the operational flexibility of conventional FCC processes.
Thus, it would be desirable to develop a FCC process which avoids the aforementioned disadvantages of conventional FCC processes.